ChEBI entity of the month: S-Propyl propanethiosulfinate and plants
As part of a newly-discovered defence mechanism, the roots of some plants have been found to release the foul-smelling sulfur compound S-propyl propanethiosulfinate when they are disturbed by potential predators. ChEBI's 'entity of the month' explains.
Many plants are famed for their putrid smells, and it has been known for decades that unpleasant sulphurous odours are released when soil is disturbed around the roots of some plants. It has always been assumed that these odours are released passively as a result of tissue damage. Now a team of researchers led by Dr. Rabi Musah at the University at Albany in New York has discovered a previously unknown defence mechanism in plants: roots that actively release a foul odour when they sense the touch of a potential predator [1].
Studies were performed using Mimosa pudica, a perennial shrub native to Brazil but now widely distributed throughout the world. Its roots are known to emit a cocktail of small organic and inorganic sulfur compounds into the environment, but with no detectable odour. However, when soil around the roots is dislodged or when seedling roots are touched, a distinctive odour is detected. By using high-resolution mass spectrometry techniques, the researchers were able to attribute the odour to the emission of increased amounts of S-propyl propanethiosulfinate (CHEBI:91021), propanesulfenic acid, 2-aminothiophenol and phenothiazine.
Plants may be smarter than you think!
The team also observed that the roots seemed to distinguish between different kinds of touch. While touching the roots with soil or human skin elicited a strong odour, agitating the roots with other materials such as glass or metal did not induce a similar response. Finally, by growing seedlings of M. pudica in a sterile environment, the team were able to ascertain that emission of the organosulfur volatiles occurred exclusively from the roots and not the aerial parts of the plant. The team have also found that at least six other Mimosa species produce the same smell and now plan to study plants in the closely related Acacia genus.
Pictured: A Creative Commons-licensed photograph of the purple flower head of Mimosa pudica., taken from Wikimedia Commons.
Reference
Musah RA, Lesiak AD, Maron MJ, et al. (2015) Mechanosensitivity below ground: touch-sensitive smell-producing roots in the "shy plant," Mimosa pudica L. Plant Physiol pii:01705.2015 [Epub ahead of print]
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